1. Field of the Invention
The invention generally relates to non-tracking solar energy collector systems and more particularly to a collector system characterized by an improved solar energy concentrator having a plurality of independently supported asymmetric reflector modules for directing incident beams of solar energy on segments of a vacuum-jacketed receiver arranged in parallelism.
2. Description of the Prior Art
Currently, substantial quantities of time and funds are being devoted to a search for sources of energy which can be utilized to replace more conventional sources of energy, such as fossil fuels.
It has long been recognized that the sun provides a substantially endless source of energy. For example, it has long been recognized that a conversion of solar energy to other forms of usable energy can be achieved simply by converting solar energy to steam which is, of course, usable for numerous purposes including the generation of electrical power. Moreover, systems employed in converting solar energy to more useful forms of energy normally are considered to be simple and economic to fabricate and maintain. These recognized advantages have led many investigators toward further development of solar energy conversion systems having a capability for more readily and economically converting solar energy to other usable forms of energy.
The future success of solar energy conversion systems is believed by many to be dependent in large measure upon the availability of efficient collector systems, particularly in environments in which the required temperatures are in ranges extending from approximately 100.degree. to 200.degree. C. Moreover, collector systems must be reliable in performance, require little maintenance, be relatively economic to fabricate and operate, and, finally, must be characterized by high strength-to-weight ratios which facilitate mounting of the systems in operative environments, such as on roofs of homes, in which the systems are subjected to both mechanical and thermal stresses of varying degrees of severity.
Consequently, numerous attempts have been made to improve the efficiency in performance of fixed collectors and/or to reduce the costs thereof. To exemplify, concentrators including mirror boosters have been used with varying degrees of success. Similarly, vacuum tubes and the like have been used as collectors with similar results. Unfortunately, the collectors heretofore known tend to suffer from certain undesirable characteristics. For example, mirror boosters, even vee-trough reflectors, previously employed, all require tracking and/or collector tilt adjustments in order to accommodate diurnal and seasonal changes in the relative positions of the sun. Thus the mass and complexity of known systems tend to render the use thereof undesirable from an economic standpoint.
Since non-tracking, flat-plate collectors do not require tracking or tilting, they may be said to represent the lowest capital cost per square foot of collector surface available for conversion of solar energy. However, the systems currently marketed for heating water and the like do not appear to be cost effective, particularly where the systems are relied upon to generate power on an annual basis. This apparent disadvantage arises out of the fact that performance of currently available flat-plate collectors tends to be relatively poor at elevated temperatures due to excessive heat loss from the absorber plates employed.
Among the various approaches taken in reducing radiation losses from absorber plates of flat-plate collectors operating at temperatures above 100.degree. C is to employ various coatings. It is known that convection losses, on the other hand, can be suppressed by using honeycomb cells or by providing evacuated chambers between the absorber plate and the transparent cover normally provided therefor. Unfortunately, the use of honeycomb cells tends to reduce the incoming flux by absorption and, also, increases the backward conduction. Moreover, there are potential problems inherent in plastic honeycomb materials and, of course, glass honeycombs are excessively expensive.
Reduction of convective losses through a use of evacuated chambers requires the use of good seals in order to maintain the required levels of vacuum during the lifetime of the system within which the seals are employed. Such seals are, of course, often difficult to maintain. Furthermore, it should be appreciated that for flat-plate collectors of customary dimensions, a transparent cover must be supported by suitable members, referred to as pegs, in order to eliminate stress-induced cracking resulting from forces occurring due to atmospheric pressures. These pegs, unfortunately, also tend to increase conduction losses. Furthermore, even though plastic covers offer some advantages over glass, from a stress standpoint, operational problems such as scratching, distortion and even melting under static conditions and degassing under vacuum are encountered.
Recently, evacuated tube collectors using borosilicate glass tubes have been suggested for use in non-tracking solar heat collector systems. Moreover, glass to metal vacuum seals apparently capable of being employed over long periods of time, without experiencing undesirable degradation, have been employed with these tube collectors. As a consequence, vacuum tubes tend to present a number of advantages over conventional flat-plate designs, from both a thermal performance and a longevity viewpoint. Unfortunately, however, when employed in non-tracking flat-plate systems, the economics costs of vacuum tubes are substantially greater than those of conventional flat-plate systems and thus render the resulting energy excessively expensive.
Since no existing system has provided a practical solution to the problem of providing for satisfactory cost effectiveness in systems capable of converting solar energy to more usable energy forms, in practical quantities, there currently exists a need for a non-tracking solar energy system which is simple and economic to fabricate, substantially efficient in operation and characterized by low initial and operational costs.